The present invention generally relates to a a linear driving apparatus for moving an optical mechanism and so on of a duplicating machine.
A duplicating machine of a document-stand fixing system and duplicating machines of a electronic photographic systems are provided with a linear driving apparatus which is adapted to alternately move an optical mechanism including an optical mechanism for drum projection use and an optical mechanism for document scanning use in a document scanning method.
The conventional linear driving apparatus is adapted to use two units of linear motors so as to cope with the higher speeds of the recent duplicating machines. The optical mechanism is adapted to move the optical mechanism at the given speed pattern through the linear motors. The electric construction of controlling the linear motors will be described with reference to FIG. 6.
A control circuit 10 mainly including microcomputers of so-called software servo compares the data on the movement position of the optical mechanism, which have been introduced through the feedback signals, with the feedback signals from the encoder 40, which have been disposed in the linear driving portion 30 as the linear motor is inputted into the control circuit 10, with the data on the speed pattern of the optical mechanism accommodated previously in the ROM and so on to generate the PWM signals in accordance with the comparison results. The PWM signal is introduced into a driving control portion 20, where the PWM signal is actually converted into an electrical signal for driving the linear driving portion 30 so as to respectively move the optical mechanisms as the speed pattern instructs. However, as shown in FIG. 3, the speed pattern of the optical mechanism is adapted to return the optical mechanism as far as the initial position at a high acceleration after the optical mechanism has been moved from the initial position at the constant speed.
However, in the above-described conventional embodiment, there is caused a following problem in the promotion of the higher speed of the duplicating machine. Namely, in order to shorten the time required for the duplicating operation, the acceleration is required to be set higher in the returning operation of the optical mechanism and so on, in other words, the driving output of the linear driving portion 30 is required to be increased. The considerable difference is caused between the constant speed condition and the high speed condition in the driving output of the linear driving portion 30. As a result, there is a disadvantage in that the speed control in the constant condition becomes rough so as to vary the speed and to cause noises. When the driving output of the linear driving portion as compared with that of the constant speed condition, the weight per bit of the PWM signal to be generated in the control circuit 10 has to be set higher, so that the closer control cannot be set in the constant speed condition. Such a disadvantage becomes an extremely large hurdle in the promotion of the higher speed of the duplicating machine.